1. Field of the Invention
The present invention generally relates to a rotary drive member such as a wheel, pulley or gear that can be mounted on a shaft for transferring torque typically to and from the shaft. More particularly, the present invention relates to a rotary drive member such as a wheel, pulley or gear that is formed by injection molding plastics material in a mold that contains one or more preform inserts so that the molded plastics material envelops selected portions of the preform insert or inserts. Preferably the insert or inserts are formed from metal such as steel, and the rotary drive member is a pulley that has a hub and a rim, with one of the inserts being a sleeven-like member that defines hub portions which are engageable with and mountable on a shaft, with the other insert being an annular disc that forms a web which interconnects the hub and the rim, and with the molded plastics material defining a toothed drive formation on the periphery of the rim.
2. Prior Art
Rotary drive members such as wheels, pulleys and gears that are mountable on a shaft for rotation about the axis of the shaft typically have been formed either from metal or from injection molded plastics material. Forming a rotary drive member from metal has the advantage of providing a strong, rigid structure that can be configured to transfer relatively large torque for example between a shaft on which the drive member is mounted and another drive member such as a gear or an endless belt that engages the rotary drive member. Forming a rotary drive member from injection molded plastics material has the advantage of providing a relatively lightweight structure that is formed at relatively low cost.
It is known also to form one or more parts of a rotary drive member such as a pulley from injection molded plastics material, and to use the molded part or parts in combination with one or more separately formed metal parts to provide a rotary drive member that is an assembly of plastic and metal components. For example, the referenced Variable Pitch Pulley Patent discloses the use of separately formed metal and plastic parts to provide a pulley that has a sleeve-like hub liner which has a non-circular outer surface that drivingly engages matingly configured hub portions of a pair of disc-like sheaves that are formed from plastics material. The metal hub liner is defined by an elongate sleeve-like part having a circular inner surface that is configured to receive a shaft on which the hub of the pulley can be mounted. The sheaves are movable relative to each other to define a belt-receiving groove therebetween that is of adjustable width for receiving an endless V-belt. The adjustable spacing of the sheave structures enables the pulley to assume different effective pitch diameters for drivingly engaging a V-belt.
In the preferred practice of the invention of the referenced Variable Pitch Pulley Patent, a selected one of the sheaves is rigidly connected to the metal hub liner (and to a shaft on which the pulley is mounted) by threaded fasteners such as set screws that extend through aligned holes which are formed in the metal hub liner and in an adjacent hub portion of the selected sheave. A variety of other devices for connecting wheels, gears, pulleys and the like to shafts are known, including keys that extend in aligned keyway formations, and pins that extend through aligned holes. The referenced Clamped Pin Connection Patent discloses still another connection method that uses a crimped endless band to force a hardened pin point into the material of a shaft to establish a driving connection between the shaft and a gear or pulley that is carried on the shaft.
It has long been accepted by those skilled in the art that if components of metal and plastics materials are to be utilized together to form a rotary drive member, these components should be preformed separately and then assembled. However, because the separate forming of mating metal and plastic components requires the accurate forming of mating configurations that will fit together snugly in order to establish proper driving connections, the high cost and difficulty of properly forming and assembling wheels, gears and pulleys that are made from a combination of metal and plastic parts often has precluded the use of such assemblies.